|By Linda Sieg and Hyonhee Shin

|By Linda Sieg and Hyonhee Shin

|By Linda Sieg and Hyonhee Shin

|By Linda Sieg and Hyonhee Shin

TOKYO/SEOUL (Reuters) - Japan's foreign minister said on Wednesday he personally regretted the departure of "frank, trustworthy" U.S. Secretary of State Rex Tillerson ahead of a proposed summit between President Donald Trump and North Korean leader Kim Jong Un.

Trump fired Tillerson on Tuesday after a series of public rifts over policy on North Korea and other issues, replacing him with loyalist Central Intelligence Agency Director Mike Pompeo.

"He (Tillerson) was a frank, trustworthy counterpart and I thought we would deal with the North Korea issue together, but personally, I feel that this situation that has developed is unfortunate," Japanese Foreign Minister Taro Kono told reporters in Tokyo.

"For sure, America holds the key, so I want to meet his successor as secretary of state soon and exchange views on North Korea and other matters," Kono said.

Critics expressed dismay at the decision to swap out top diplomats so soon before the unprecedented potential meeting between Kim and Trump, and worried that Pompeo would encourage Trump to be hawkish on North Korea.

South Korea's Foreign Minister Kang Kyung-wha decided to go ahead with a planned trip to Washington to discuss North Korea despite Tillerson's departure, the ministry said in a text message. An official had earlier said she would cancel the visit.

Other South Korean officials, also speaking on the condition of anonymity, said that while Pompeo was known to have hardline views on North Korea, he was a seasoned politician and seemed to know how to compromise.

"We're aware that Pompeo was one of the strongest voices in the talk of military action and fed Trump related assessments, but things have since changed a lot," one senior official said, referring to upcoming inter-Korean talks and the prospect of a Kim-Trump summit. "So, we will see."

Chinese Foreign Ministry spokesman Lu Kang said China hopes the change in personnel will not impact the development of relations and important areas of cooperation.

"We of course hope that the positive momentum on the Korean peninsula, including the political will for talks of both the United States and North Korea, will be maintained," Lu told a daily news briefing.

CHINA CONTACT CRUCIAL

Shares in Japanese defense equipment makers rose sharply on speculation that geopolitical tensions may rise after the firing of Tillerson and Pompeo's appointment. Ishikawa Seisakusho surged as much as 15 percent, while Howa Machinery jumped 11 percent.

Jia Qingguo, an expert on Chinese diplomacy at Peking University in Beijing, said China may see positive outcomes from the change when it comes to the U.S. position on the Belt and Road initiative, Chinese President Xi Jinping's signature foreign policy initiative.

"Tillerson has at times been quite critical of China, including of Belt and Road," Jia said. "Trump is not as hawkish on China as many assume. He has tried to communicate and to cut a deal."

Coming from the CIA, Pompeo is more likely to see China as a threat but his views will probably soften, Jia said.

"Once you are in the secretary of state position, you need to be more pragmatic and take into account the huge stakes involved, so the impact will not be as big as some people expect."

Most important for China was that Pompeo makes contact with his Chinese counterparts to ensure a smooth meeting between Kim and Trump as soon as possible, said Ruan Zongze, a former Chinese diplomat now with the China Institute of International Studies, a think tank affiliated with the Foreign Ministry.

"Time is short. There are a lot things to do. Every day is very important," he said.

Pompeo is also known for his hawkish views on trade. He takes over as the chief U.S. diplomat as the United States is finalizing the imposition of hefty tariffs on steel and aluminum that have upset a number of Asian trading partners.

Close ally Australia, which is working through an exemption from the U.S. tariffs, welcomed Pompeo's appointment.

"We know him very well," Prime Minister Malcolm Turnbull told reporters. "He's a great friend of Australia. The transition will be absolutely seamless. Our relationship with the United States, as you know, is outstanding at so many levels from the president and myself, right through the military, intelligence, diplomacy and business."

South Korea is the largest supplier of steel to the United States not to have secured an exemption from the tariffs and is facing pressure from Trump over the two countries' free-trade deal.

"It is our joint understanding with the United States that strong cooperation be maintained through close communication between South Korea and the United States regardless of U.S. personnel changes as there are important issues, including the North Korea nuclear issue, the U.S.-South Korea alliance and trade matters," South Korea's Foreign Ministry said.